Thermostatic switch



Aug. 30, 1960 H. n. EPSTEIN THERMOSTATIC SWITCH Filed Dec, 24, 1958 United States iatefnt @ffice 2,951,137 Patented Aug. 30, 1960 THERMOSTATIC SWITCH Henry David Epstein, Cambridge, Mass., assignor to Texas Instruments Incorporated, Dallas, rTex., a corporation of Delaware Filed Dec. 24, 1958, Sel'. No. 782,895

3 Claims. (Cl. 20G-113) This invention relates to thermostatic switches, and with regard to certain more specic features to snap-acting switches of this class.

Among the `several objects of the invention may be noted the provision in a compact, simple structure of a snap-acting thermostatic switch adapted for push-pull manual circuit-closing and opening operations; the provision of a thermostatic switch which is of the manual reset type but which is trip free; and the provision of a switch of this class which will indicate an open or closed circuit condition whether induced manually or automatically in response to temperature change. Other objects and features will be in part apparent and in part pointed out hereafter.

The invention accordingly comprises the elements and combinations of elements, features of construction, and arrangements of parts which will be exemplified in the structures hereinafter described, and the scope of which will be indicated in the following claims.

In the accompanying drawings, in which one of the various possible embodiments of the invention is illustrated:

Fig. l is a top plan View of the switch, parts of a framework being broken away and shown in section;

Fig. 2 is a section taken on line 2-2 of Fig. l, parts being shown in elevation;

Fig. 3 is a fragmentary view similar to Fig. 2 but showing an alternative position of parts; and

Fig. 4 is a view similar to Fig. 3 showing another alternative position of parts. i

Corresponding reference characters indicate corresponding parts throughout the several views of the drawings. The dotted lines in Fig. 2 illutrate open-circuit positions of certain parts.

Referring now more particularly to the drawings, there is shown at numeral 1 an insulating framework which has attached to it a pair of separate line terminals 3 and 5. Rivets for the purpose are shown at 7 and 9, respectively. Rivet 7, which is conducting, has conductively connected therewith a xed contact 11. Threaded through the terminal is a conductive post or support 13 adapted through a screwdriver slot 15 to be adjusted in position. The upper end of the post 13 is provided with a shoulder 17 and a washer 18 held in place by a headed over or staking end portion 19 of the post 13, to provide a conventional close fitting but rotatable mounting for a snap-acting thermal element 23. The arrangement is such that a good electrical connection is provided between support 13 and element 23. The washer 18 may be hexagonal as shown, whereby, in View of the staking with the headed part of post 13, the post may also be adjusted by use of a wrench on the staked washer.

At 23 is shown a resetting type of bimetallic or composite-metal snap-acting thermostatic plate or disc from which extend opposite ears 25 and 27. Its component of high coefficient of expansion is shown at 2. Its component of lower coefficient of expansion is shown at 4.

Attached to ear 25 is a movable contact 29 engageable and disengageable with the fixed contact 11. In the opposite ear 27 is an opening 31. The disc 23 during its manufacture is deformed in known manner to 'assume a shape which renders it snap-acting in moving from its solid-line position to its reversely curved dotted-line position (see Fig. 2). The dotted-line position may be obtained by temperature change (caused by heating herein), or by application of force (manually herein) regardless of temperature change. However, being of the resetting type, movement from the dotted-line to the solid-line position can be `accomplished only by application of force and not by temperature change (cooling herein) to which the device will normally be subjected. The plate 23 is treated during manufacture in known manner such that the stated functions occur. Such treatment for the purpose is known in the art.

The plate is provided with a relief opening or slot 33 preferably of more or less semicircular shape surrounding a central portion 35. This central portion constitutes an anchoring tongue in which is located an opening 37 adapted for the reception of the upper portion of the post 13 and thereafter application of the washer 18. It is by this means that the plate is rigidly but rotatably mounted upon the post as shown in the drawings. This mode of mounting upon an interiorly relieved portion of the plate (central portion 35) allows for movements between the solidand dotted-line positions shown in Fig. 2 or the tilting movements ilustrated in Figs. 3and 4. Because of the aforementioned rigid connection between post and disc, such motions would not be attainable except for the tongue 35.

Threaded throughan overhanging portion 39 of the frame 1 is an adjustable stop screw 41 located above the ear 25. The overhanging portion 39 is also provided with an opening 43 for the freely sliding reception of an insulating button or control member 45 having a push-pull type of head 47. The button is provided with a distinguishing colored (say black) band 49 and a second distinguishing colored (say white) band 51. The band 51 is hidden when the button is pushed in and exposed when the button is pulled out. The button 45 is provided at its lower end with a bushing insert 53 -for the adjustable reception of a threaded screw 55. p

The shank of the screw passes through the opening 31. Its head 57 is larger than the opening 31 and is exposed behind an opening 6 forming access for adjustmer. Around screw 55 `and located between the ear 27 and bushing 53 is a loose spacer collar 59. The arrangement as shown by the drawings provides a loose or lost-motion connection between the control button 45 and the marginal ear portion 27 of the plate or disc element 23.

In the solid-line (cold) position of the plate 23 as shown in Fig. 2, the circuit is closed through terminals 3, 5, contacts 11, 29, plate 23 and post 13. In this condition the colored band 51 is hidden in the overhanging portion 39, thus exposing only the colored band 49 to indicate that the circuit is closed.

Upon heating the plate 23 a predetermined amount, by current flow through it and/ or by ambient temperature conditions, the plate will snap from the solid-line position shown to the dotted-line position (Fig. 2), thus rapidly withdrawing contact 29 from contact 11 and opening the circuit. This also has the effect of pushing out the freely movable button 45 so as to expose the colored band 51 to View beyond the portion 39. This indicates that the circuit is open. Without further manipulation, the open-circuit condition will be maintained with or Without cooling within the ambient temperature range to which the device is normally subjected. This is due to the manual reset characteristics of plate 23.

After cooling, button i5 may be manually pushed in, whereupon plate 23 will pass through the transitory condition shown in Fig. 3. In this condition, portions surrounding the central anchor 35 will become deformed and tilted anticlockwise as shown, with ear 27 pushed down by ring 59 and ear 25 pushed up against stop lll. The axis of the tilt is located on line A-A (Fig. l). The induced reactions consist of downward forces on the ears 25 and 27 with upward reaction centrally applied by the post 13. The resultant stresses in the plate snap it back to the solid-line closed position shown in Fig. 2. This action constitutes manual reset from an open cold position.

It is to be observed that, if any attempt is made to reset from the dotted-line position of plate Z3 in Fig. 2 to its solid-line position therein while the plate is hot, i.e., to send it beyond the shape shown in Fig. 3, circuit reclosure will not occur. This is because driving the plate into the Fig. 3 position while hot will not stress it enough to have it snap. lt then remains xed in the Fig. 3 position as long as button 45 is held in and until cooling occurs while the button is so held in. lf cooling occurs While the button is pushed in, the circuit will reclose. I-f the button is released before cooling occurs, return to the dotted-liiie position of Fig. 2 will result. The switch is trip-free because with the above constructions, there is nothing to prevent the device from snapping to the contact open position when heated, regardless of the position of button 45.

lf it is desired manually to open the circuit from its solid-line closed position shown in Fig. 2, the button 45 is pulled out. rl`his drives plate 23 through its transitory condition shown in Fig. 4. In this condition the portions of the plate 23 which surround the anchor 35 again become deformed but tilted clockwise around line A-A in Fig. 1. The tilt increases pressure between contacts 29 and llll. The induced reactions are upward forces under the ears 25 and 27 with a downward central reaction on the plate from the post 113. This results in stressing the plate until it snaps from the solid-line position shown in Fig. 2 to its dotted-line position shown in that ligure. This manual opening action can occur at any point up to the temperature induced snapping of the element 23.

lt will be understood that heating of the plate 23 while the circuit is closed may be brought about by excess current llowing through it or by ambient temperature rise, or both. Heating while open is possible only by ambient temperature change.

in view of the above it will be seen that the plate 23 automatically responds to temperature increase to open the circuit and maintains an open circuit whether or not subsequent cooling occurs. The plate 23 may also be manually pulled into such open-circuit condition. In either case the button 45 indicates this open circuit condition. Manual resetting may be elected only when the disc is cold, regardless of which of the above methods is employed for opening. Thus, the switch is both indicating and of the manual reset type. If, after the circuit has opened by movement of the disc to the dotted-line position shown in Fig. 2, the disc fails to cool, then a manual resetting operation becomesV inelective to close the circuit.

Regarding line A-A in Fig. 1, it is to be noted that it is drawn through the approximate terminal portions of the slot 33, which partially separates the center anchor portion 35 of the plate 23 from its snap-acting peripheral portions. The fact that the peripheral portions are more or less free from the anchor 35 accounts for their ability to tilt around line A-A. In general, the shorter the slot the less the tilt, and vice-Versa. The arrangement shown is such that the amount of tilt of ear 27 caused by pushing or pulling action on the ear 2.7 from button 45, in order to efrect snap-action (see Figs. 3 and 4) shall be less in amount than the free snap movement of this ear (see Fig. 2). Likewise the tilting movement of ear 25 in order to bring about snap action is less than the free snap movement of this ear. Also, the free snap movement of the ear 27 moves the button 4S suiciently to indicate openor closed-circuit condition by means of the distinguishing bands 49, 51.

lt will be understood that, while'the semicircular slot 33 is shown herein for permitting tilt between the marginal area of the thermostatic plate 23, other shapes of slot may be employed for the purpose.

ln view of the above, it will be seen that the several objects of the invention are achieved and other advantageous results attained.

As various changes could be made in the above constructions without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

I claim:

l, A push-pull manual reset thermostatic switch of the trip-free type comprising a framework, spaced insulating conductive terminals carried thereon, a conductive support extending from one terminal, a xed Contact extending from the other terminal and spaced from one side of the support, a ilexible manual reset type thermostatic conductive plate having a iiexibly connected interior portion within its marginal area carried on Said support, said marginal area being Vsubstantially tiltable relative to said interior portion and being snap acting,

a movable contact carried on one side of the marginal area of said plate adapted for engagement and disengagement with respect to said fixed contact, a bacltstop carried by said framework in spaced relation to said fixed contact, a substantially freely movable control member having switch-open and switch-closed positions, and an operating push-pull connection between said control member and a marginal portion of said plate which relative to said support is opposite to said movable contact, whereby opposite tilts of said marginal area by push-pull operation of the control member will force the movable contact portion of said marginal area against the stop or the ixed contact with reaction from the framework to snap 'act the marginal area to marginally engage or disengage said contacts, said plate in the absence of push or pull operation of the control means being adapted substantially freely to snap act in response to temperature change to disengage said contacts and to move said control member to its switch-open position, the arrangement being such that the movements of said marginal areas at the movable contact and at said connection are less for push-pulloperation than the free snap movements of these last-named areas.

2. A push-pull manual reset thei'mostatic switch of the trip-free type according to claim l, including indicating means on said control member operable by manually or thermostatically induced movements of said plate adapted positively to indicate engagement or disengage-V ears carried by said disc, a movable Contact carried byl one ear adapted for engagement and disengagement with respect to :said xed contact, a backstop carried by said framework in spaced relation to said fixed contact, a control but-ton substantially freely movable with respect to the framework and having switch-open and switchclosed positions, cooperative index'means between the button and a fixed part of the framework adapted upon movement of the button positively to distinguish between said positions, and an operating lost-motion pushpull connection between said control member and the other ear of the disc, said other ear relative to said support being opposite the ear which carries the movable contact, whereby opposite tilts of said marginal area by push-pull operation of the control member will force said movable contact against the -iixed contact or stop with reaction from the framework to snap act the marginal area to manually engage or disengage said contacts, said disc in the absence of push-pull operation of the control member being adapted freely to snap act in response to temperature change to disengage said contacts and 4to move said control member to its switch-open position, the arrangement being such that the tilt movements of said ears are less than their free snap movements.

References Cited in the file of this patent UNITED STATES PATENTS '2,157,857 Lee May 9, 1939 2,182,048 Elmer Dec. 5, 1939 2,361,162 Arnold Oct. 24, 1944 2,363,280 Arnold Nov. 2l, 1944 2,420,300 Cataldo et al May 13, 1947 2,624,819 Spina et al. Jan. 6, 1953 2,828,386 Malone Mar. 25, 1958 

